International Encyclopedia of Systems and Cybernetics

Unplanned results of a planned change in a process or system.

(also known as "spillover effects" (J.van GIGCH, 1978, p. 153).

Side effects are a typical result of non-systemic misunderstanding of complex issues.

They are a frequent result of planning based on linear methods, without regard to complexity in processes. Side effects are nearly always unexpected and surpressive, because they generally emerge outside of the scope of the development considered. They become more and more frequent with the ever wide-embracing nature of man's interventions in natural processes. While they are not necessarily negative, they should be as much as possible preventively monitored.

Moreover, in fact many side effects could be considered "wicked" ( the french "effets pervers" of the sociologist Raymond BOUDON), because they frequently derive from appearently positive steps taken to solve or alleviate serious problems.

Some recent examples are: newly acquired resistance of pathological agents to antibiotics and of pests to pesticides; massive and unmanaged rural emigration caused by the green revolution; disastrous spills resulting of massive oceanic transportation of oil; social and urban transformations due to massive use of cars. The key word is "massive"! Many more cases could be cited and still more are undoubtedly in the making.

Such counter-intuitive messes are results of a partial and out of space and time context approach to the addressed issues

The systemic study of the complex interactions of any system with its environment – as a complex whole itself – should be very helpful to forecast and prevent such situations. Side effects have enormous ethical bearings, fully described by J.van GIGCH (Ibid).